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Thermochemical flows couple the Earth's inner core growth to mantle heterogeneity

Nature volume 454, pages 758–761 (2008)Cite this article

Abstract

Seismic waves sampling the top 100 km of the Earth's inner core reveal that the eastern hemisphere (40° E–180° E) is seismically faster1,2, more isotropic2,3 and more attenuating4 than the western hemisphere. The origin of this hemispherical dichotomy is a challenging problem for our understanding of the Earth as a system of dynamically coupled layers. Previously, laboratory experiments have established that thermal control from the lower mantle can drastically affect fluid flow in the outer core5, which in turn can induce textural heterogeneity on the inner core solidification front6. The resulting texture should be consistent with other expected manifestations of thermal mantle control on the geodynamo, specifically magnetic flux concentrations7,8 in the time-average palaeomagnetic field9,10 over the past 5 Myr, and preferred eddy locations11 in flows imaged below the core–mantle boundary by the analysis of historical geomagnetic secular variation12. Here we show that a single model of thermochemical convection and dynamo action can account for all these effects by producing a large-scale, long-term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle. The main feature of this thermochemical ‘wind’ is a cyclonic circulation below Asia, which concentrates magnetic field on the core–mantle boundary at the observed location and locally agrees with core flow images. This wind also causes anomalously high rates of light element release in the eastern hemisphere of the inner core boundary, suggesting that lateral seismic anomalies at the top of the inner core result from mantle-induced variations in its freezing rate.

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Figure 1: Time-average flow structure of model case I.
Figure 2: Comparison between model and observations.

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Acknowledgements

J.A. was supported by the SEDIT programme of CNRS-INSU. H.A. was supported by a Marie Curie intra-European grant. Numerical calculations were performed at the Service de Calcul Parallèle, IPGP, and at IDRIS, France. We thank S. Tanaka for providing published data, and V. Cormier for discussions. This is IPGP contribution 2369.

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Authors and Affiliations

  1. Dynamique des Fluides Géologiques,,

    Julien Aubert

  2. Géomagnétisme, Institut de Physique du Globe de Paris, Université Paris-Diderot, INSU/CNRS, 4, Place Jussieu, 75252, Paris cedex 05, France ,

    Hagay Amit & Gauthier Hulot

  3. Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA,

    Peter Olson

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  1. Julien Aubert
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  4. Peter Olson
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Correspondence to Julien Aubert.

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The file contains Supplementary Discussion and Supplementary Figure 1.with Legend. The file includes information about model assumptions, scaling relationships and the choice of model parameters. (PDF 1424 kb)

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Aubert, J., Amit, H., Hulot, G. et al. Thermochemical flows couple the Earth's inner core growth to mantle heterogeneity. Nature 454, 758–761 (2008). https://doi.org/10.1038/nature07109

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